In a thermal power plant or the like which uses a large amount of fossil fuel, exhaust gas generated when the fossil fuel is burned in a boiler contains CO2 and the like. As a method of eliminating and recovering CO2 contained in exhaust gas, there is a method of bringing the exhaust gas into gas-liquid contact with an amine CO2 absorbing solution to absorb CO2 in the CO2 absorbing solution. Then, the CO2 is released from the CO2 absorbing solution having absorbed the CO2, and the released CO2 is stored in the ground, thereby preventing the CO2 recovered from the exhaust gas from being released into the atmosphere.
For example, there is proposed a CO2 recovering apparatus that recovers CO2 from exhaust gas by using CO2 absorbing solution and stores CO2 recovered from the exhaust gas along the way (for example, see Patent Literature 1). The CO2 recovering apparatus includes a CO2 absorber that allows the exhaust gas to contact a CO2 absorbing solution and allows the CO2 absorbing solution to absorb CO2 contained in the exhaust gas, and a regenerator that releases CO2 absorbed by the CO2 absorbing solution and separates CO2 from the CO2 absorbing solution. This CO2 recovering apparatus causes the CO2 absorber to absorb the CO2 contained in the exhaust gas in the CO2 absorbing solution and eliminates the CO2 from the exhaust gas, and then causes the regenerator to heat the CO2 absorbing solution with vapor, thereby releasing the CO2 absorbed by the CO2 absorbing solution and recovering high-purity CO2. Further, the CO2 absorbing solution regenerated by the regenerator is fed to the CO2 absorber again and is recycled.
In this CO2 recovering apparatus, CO2 and a small amount of H2O are flown out of the regenerator. In order to keep the liquid amount of the absorbing solution in a space between the CO2 absorber and the regenerator (hereinafter referred to as “system space”) at a certain amount, makeup water is added to the system space or the condensation amount of water contained in the exhaust gas within the CO2 absorber is adjusted. The condensation amount of water contained in the exhaust gas within the CO2 absorber is controlled by, for example, a method of adjusting the cooling ratio of the exhaust gas by using a cooling tower or the like provided at the upstream side of the absorber, or a method of adjusting the cooling temperature of the CO2 absorbing solution within the CO2 absorber.
In the CO2 recovering apparatus, the absorber or the regenerator is provided with an absorbing solution level meter and a level controller, and the condensation amount of water contained in the exhaust gas or the supply amount of makeup water is adjusted to thereby maintain the liquid level at a constant liquid level.